PSI - Issue 53

Reza Ahmadi et al. / Procedia Structural Integrity 53 (2024) 97–111 Author name / Structural Integrity Procedia 00 (2019) 000–000

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raster angle on the overall fatigue strength of additively manufacture d (AM) polylactic acid (PLA) can be disregarded with minimal loss of accuracy. In (Hassanifard & Behdinan, 2023)the fatigue strength of notches 3D-printed polylactic acid (PLA) samples was investigated through experimental analysis. The findings demonstrated that the pre-existing discontinuities within the filament structure behaved similarly to sharp notches. In another study(Guillermo et al., 2023) notch sensitivity in u-notched 3D printed polymers was investigated and it was concluded that the number of cycles to fracture of material increased as the notch radius increased and vice versa. There are also some studies on the impact of pre-existing notches within 3D-printed components on fatigue performance(Brenne & Niendorf, 2019; Razavi et al., 2018). In this research, we utilized thermographic measurements on the surface of specimens subjected to static loading conditions. Our goal is to comprehensively examine the development of damage within these specimens and to delve into this phenomenon from both mechanical and energetic standpoints. Our focus is on notched specimens, specifically within the realm of applications like scaffold structures. Through this study, we investigate the fatigue characteristics of notched 3D-printed PLA materials, taking into consideration two different notch geometries. Furthermore, through the integration of Ansys Composite Pre-Post (ACP) simulation, we delve deeper into understanding the intricate material behavior and performance of 3D printed PLA specimens to establish a systematic framework that can refine the accuracy of design processes in this field. 2. Static Thermographic Method background Principles Infrared thermography, often referred to as IR-thermography, is a non-destructive technique (NDT) that finds extensive use in temperature measurements and damage detection. Considering conventional fatigue tests, which necessitate testing a substantial number of specimens, STM offers the advantage of swiftly evaluating the fatigue properties of a material using only a limited number of specimens. It operates on the principle of detecting electromagnetic radiation emitted by a part, which is influenced by its thermal state. This method enables contactless measurement of a body's surface temperature. IR-thermography is a valuable tool for conducting non-destructive analyses (NDAs) on various materials and components. It is employed to identify damage resulting from mechanical loading or thermal stress, as well as defects that may arise during the manufacturing process. In addition, IR thermography serves as a valuable tool for stress analysis, with one of its notable applications being Thermoelastic Stress Analysis (TSA). TSA is an experimental method employed for stress evaluation, relying on the thermoelastic effect as its foundational principle.(Emery et al., 2008; Emery & Dulieu-Barton, 2010; Gallotti & Salerno, 2007; Libonati & Vergani, 2013; Salerno et al., 2009). IR-thermography is also extensively utilized for investigating the fatigue behavior of homogeneous materials.(Fargione et al., 2002; La Rosa & Risitano, 2000) The fundamental premise of the Static Thermographic Method (STM) revolves around assessing the concluding phase of thermoelastic behavior during a static tensile test of a material. Furthermore, valuable insights into the material's fatigue behavior can be extracted from these static tests. In the context of uniaxial traction tests, commonly employed in engineering, the temperature variations over time, as detected by an infrared camera, generally manifest in three distinct phases. In 2013, Risitano and Risitano (Risitano & Risitano, 2013)conducted research elucidating these phases during a static tensile test and introduced an innovative methodology for determining the damage stress of materials under monaxial tensile conditions. Phase I is characterized by a linear decrease in temperature attributed to the thermoelastic properties expounded by Lord Kelvin's law. Phase II ensues with a declining temperature trend, albeit distinct from Phase I. As Phase II nears its conclusion, the temperature stabilizes, forming a plateau that correlates with the material's yielding stress. Phase III marks the ascendancy of plastic damage over elastic behavior, leading to a temperature increase until eventual specimen failure. The point of transition from Phase I to Phase II signifies the initiation of irreversible damage within the material. By delineating regression lines for temperature data in these two phases and identifying their intersection, it becomes possible to ascertain the material's damage stress as shown in Figure 1.